1. Field
The present disclosure broadly relates to fabrication of fiber reinforced composite laminates, and deals more particularly with a method of laminating composite tape over edges having convex radii.
2. Background
Composite laminate structures such as those used in the automotive, marine and aerospace industries may be fabricated using automated composite material application machines, commonly referred to as automated fiber placement (AFP) machines. AFP machines may be used in the aircraft industry, for example, to fabricate structural members and skin assemblies by wrapping relatively narrow strips of slit prepreg tape known as “tows”, collimated into a wider band around a manufacturing tool or other substrate. AFP machines have a material application head that includes a plurality of tape control modules which align, cut and place the tape strips, typically six or more, “on-the-fly” under numeric control. The tape strips are aligned in continuous, edge-to-edge contact forming a single wide conformal bandwidth which is compacted against the tool using a compaction device such as a compaction roller or a shoe.
The plies forming the laminate structure may be made up of plies have differing fiber orientations, such as 0°, 45° and 90° plies, with each ply being formed by multiple courses of a conformal bandwidth of tape strips placed by the AFP machine. In some cases, depending upon the shape of the part, the substrate (e.g. the tool) may have one or more radius edges over which the tape strips must be applied and compacted. However, a problem sometimes exists where it is necessary to apply the tape strips at an angle, such as a 45° angle, over an edge having a relatively sharp, convex radius, such as a 90° convex radius. As the compaction device moves over the radius edge at an angle, the trailing edge of the conformal bandwidth of tape strips just laid before the radius edge may be lifted away from the substrate by continued movement of the compaction device over the radius edge, resulting in voids or wrinkles in the plies which can adversely affect the quality of the completed structure.
Accordingly, there is a need for a method of laminating composite tape over convex radius edges that reduces or eliminates voids or wrinkles in plies caused by lifting of the tape after it has been placed and compacted.
Additionally, the plies forming the laminate structure may be made up of plies with differing fiber orientations, including fiber orientations having the standard angles such as 0°, +45°, −45°, and 90° plies, in addition to fiber orientations comprising +30°, −30°, +60°, −60° and various other angles spanning from 0° to 180° in a positive and negative direction relative to a reference, with each ply being formed by multiple courses of a conformal bandwidth of tape strips placed by the AFP machine. In some cases, depending upon the shape of the part, the substrate (e.g. the tool) may have one or more radius edges over which the tape strips must be applied and compacted. However, a problem sometimes exists where it is necessary to apply the tape strips at an angle, such as, but not limited to a 45° angle, over an edge having a convex radius, such as, but not limited to a 90° convex radius. Further, multiple differing angles of fiber orientation within laminate plies may create various angles between the fibers and lines tangent to convex radii of the laminate plies. As the compaction device moves over the radius edge at these various angles, the trailing edge of the conformal bandwidth of tape strips just laid before the radius edge may be lifted away from the substrate by continued movement of the compaction device over the radius edge, resulting in voids or wrinkles in the plies. Stated differently, the tape strips just laid immediately preceding the current position of the compaction device, at a time when the angle between the fibers and the lines tangent to the radius was slightly different than while at the current angle, the trailing edge of the conformal bandwidth may be lifted away from the substrate by continued movement of the compaction device over the radius edge, resulting in voids or wrinkles in the plies which can adversely affect the quality of the completed structure.
Accordingly, there is a need for a method of laminating composite tape over convex radius edges having various angles between fibers in the composite laminates and lines tangent to the convex radius edges that reduces or eliminates voids or wrinkles in plies caused by lifting of the tape after it has been placed and compacted.